1. Field of the Invention
This invention relates to a process for making certain haloorganosilicon compounds. More particularly, the invention relates to a process for the preparation of haloorganoalkoxysilane such as chloropropyltrimethoxysilane.
2. Description of the Related Art
Chloropropyltrimethoxysilane is a key intermediate for the preparation of a variety of amino-, mercapto- and methacryloyloxyorganosilanes which are used as silane coupling agents. Chloropropyltrimethoxysilane can also be converted into chloropropyltriethoxysilane, a key intermediate for the preparation of poylsulfane-containing organoalkoxysilanes which are used in the manufacture of silica-filled tires.
U.S. Pat. No. 6,191,297 describes a two step process involving the ethanol esterification of the product obtained from the platinum-catalyzed hydrosilation reaction of trichlorosilane and allyl chloride. This process is highly material- and plant-intensive due to low yields and significant byproduct formation, i.e., propyltrichlorosilane.
A potentially more economical route is the direct hydrosilation reaction of triethoxysilane and allyl chloride. Platinum is the most widely used hydrosilation catalyst and its use for the hydrosilation reaction of allyl chloride and triethoxysilane has been reported. According to U.S. Pat. No. 3,795,656, a 70% yield was obtained for the Pt-catalyzed hydrosilation reaction of allyl chloride and triethoxysilane. Belyakova et al., Obshch. Khim 1974, 44, 2439-2442, describes the Pt-catalyzed hydrosilation reaction of silanes with allyl chloride and reports a 14% yield for chloropropyltriethoxysilane. As disclosed in Japanese Patent No. 11,199,588, the Pt-catalyzed hydrosilation reaction of trimethoxysilane and allyl chloride resulted in a 70% yield of chloropropyltrimethoxysilane.
The primary limitation with the hydrosilation reaction of allyl chloride and a silane is a competing elimination reaction. With platinum, the competing elimination reaction is more prevalent with alkoxysilanes than with chlorosilanes. Rhodium and palladium afford primarily elimination products.
Iridium has been reported to be a very efficient catalyst for the hydrosilation reaction of allyl chloride and triethoxysilane. According to U.S. Pat. No. 5,616,762, the iridium-catalyzed hydrosilation reaction of triethoxysilane and allyl chloride is said to be very selective for chloropropyltriethoxysilane with minimal byproducts. Japanese Patent Appl. 4 [1992]-225170 reports similar results for the iridium-catalyzed hydrosilation reaction of allyl chloride and trimethoxysilane. In U.S. Pat. No. 4,658,050, the iridium-catalyzed hydrosilation reaction of alkoxysilanes and allyl chloride utilizes olefin iridium complexes.
Ruthenium has been reported to be a very efficient catalyst for the hydrosilation reaction of allyl chloride and trimethoxysilane. Japanese Patent No. 2,976,011 discloses the Ru-catalyzed hydrosilation reaction of triethoxysilane and allyl chloride to give chloropropyltriethoxysilane in about 41% yield. U.S. Pat. No. 5,559,264 describes the hydrosilation reaction of a methoxysilane and allyl chloride in the presence of a ruthenium catalyst and preferably in the substantial absence of solvent to provide a chloroalkylalkoxysilane. Tanaka et al., J. Mol. Catal. 1993, 81, 207-214 report the ruthenium carbonyl-catalyzed hydrosilation reaction of trimethoxysilane and allyl chloride and Japanese Patent Application No. 8[1996]-261232 describes the activation of ruthenium carbonyl for use as a hydrosilation catalyst for the same reaction.